The invention is directed to a pressure controlled cutter bit or drill bit retainer with a clampable cutter bit or drill bit, especially a hydraulically precision adjustable rotating drill head, with a pressure motor, comprising a base and an output sealed and resiliently mobile with respect to the base. Additionally, a mobile pressure seal, a pressure fluid chamber and a fluid supply are present, as well as an apparatus that converts motion of an output part into movement of the cutter bit on a curved path which extends approximately perpendicular to the axis of rotation.
The invention serves for solving the requirement occurring increasingly in modern manufacturing technology of fabricating internal cylinder barrel surfaces or areas as rapidly and accurately to size as possible, whole surface contour as a function of the travel of the drill bit parallel to the axis of rotation and as a function of the angle of rotation of the drill bit relative to the workpiece, deviates at most by 500 to 1,000 .mu. from an exactly cylindrical barrel or jacket surface with a tolerance in the 1 .mu.-range.+-.50%. Such untrue or out-of-center holes whose surface thus deviates polarity-wise or axially from an axially parallel straight line or from an axially concentric circle can only be imperfectly produced or manufactured by the drill bit retainers of the type being discussed here and known hitherto, which are also designated as drill heads. Assuming that the control pressure source provides the required control pressure at the right time and in the required magnitude, the mechanical actuation means of these drill heads must simultaneously have the following properties:
1. The drill or cutter bit must respond sufficiently accurately and without hysteresis effect to the control pressure; and
2. The natural frequency of the drill head must lie distinctly above the control pressure frequency. If these frequencies differ only by a small amount, then resonance effects occur which render the drill head unusable for utilization above this frequency range.
The drill heads in the state of the art fulfill either one or the other assumption. However, they do not fulfill both simultaneously.
Thus, in the drill head in U.S. Pat. No. 3,007,356, the driven end of the shaft transmits its excursion to the drill bit by means of parts rubbing against each other. Due to this friction, such a drill head cannot respond to small pressure changes whose effect does not exceed the frictional forces and also in case of larger forces, the drill bit position is not reproducibly linked with the control pressure, which has the effect that the same control pressure, depending on whether it is rising or falling, causes different drill bit positions or attitudes.
The drill heads in the teaching of DE 20 34 601-A2 and DE 22 58 553-A1 have indeed no friction and therefore produce workpieces true to dimensioning. However, their natural frequency is low because the reduced mass inertia moment referred to the drilling bit of all the parts moving relative to the base and, therefore, participating in an oscillation or vibration is large.
All drill heads in the state of the art have the additional disadvantage of comprising a large fluid chamber. With a large fluid chamber, because of the compressibility of the pressure fluid, a relatively large quantity of fluid must flow into or out of the fluid chamber through a fluid supply line offering a resistance for building up a specific pressure in the fluid chamber. Thus, a certain time is required until the pressure in the fluid chamber equals the control pressure. In the case of rapidly changing control pressure, the chamber pressure therefore deviates, as far as pressure amplitude and phase are concerned, from the control pressure upstream of the fluid supply and therefore positioning errors of the drill or boring bit occur.